/*
 * Copyright 2002-2015 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.lee.util;

import java.lang.reflect.GenericArrayType;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.WildcardType;

/**
 * Utility to work with Java 5 generic type parameters. Mainly for internal use within the framework.
 *
 * @author Ramnivas Laddad
 * @author Juergen Hoeller
 * @author Chris Beams
 * @since 2.0.7
 */
public abstract class TypeUtils {

    /**
     * Check if the right-hand side type may be assigned to the left-hand side type following the Java generics rules.
     * 
     * @param lhsType the target type
     * @param rhsType the value type that should be assigned to the target type
     * @return true if rhs is assignable to lhs
     */
    public static boolean isAssignable(Type lhsType, Type rhsType) {
        Assert.notNull(lhsType, "Left-hand side type must not be null");
        Assert.notNull(rhsType, "Right-hand side type must not be null");

        // all types are assignable to themselves and to class Object
        if (lhsType.equals(rhsType) || Object.class == lhsType) { return true; }

        if (lhsType instanceof Class<?>) {
            Class<?> lhsClass = (Class<?>) lhsType;

            // just comparing two classes
            if (rhsType instanceof Class<?>) { return ClassUtils.isAssignable(lhsClass, (Class<?>) rhsType); }

            if (rhsType instanceof ParameterizedType) {
                Type rhsRaw = ((ParameterizedType) rhsType).getRawType();

                // a parameterized type is always assignable to its raw class type
                if (rhsRaw instanceof Class<?>) { return ClassUtils.isAssignable(lhsClass, (Class<?>) rhsRaw); }
            } else if (lhsClass.isArray() && rhsType instanceof GenericArrayType) {
                Type rhsComponent = ((GenericArrayType) rhsType).getGenericComponentType();

                return isAssignable(lhsClass.getComponentType(), rhsComponent);
            }
        }

        // parameterized types are only assignable to other parameterized types and class types
        if (lhsType instanceof ParameterizedType) {
            if (rhsType instanceof Class<?>) {
                Type lhsRaw = ((ParameterizedType) lhsType).getRawType();

                if (lhsRaw instanceof Class<?>) { return ClassUtils.isAssignable((Class<?>) lhsRaw,
                        (Class<?>) rhsType); }
            } else if (rhsType instanceof ParameterizedType) { return isAssignable((ParameterizedType) lhsType,
                    (ParameterizedType) rhsType); }
        }

        if (lhsType instanceof GenericArrayType) {
            Type lhsComponent = ((GenericArrayType) lhsType).getGenericComponentType();

            if (rhsType instanceof Class<?>) {
                Class<?> rhsClass = (Class<?>) rhsType;

                if (rhsClass.isArray()) { return isAssignable(lhsComponent, rhsClass.getComponentType()); }
            } else if (rhsType instanceof GenericArrayType) {
                Type rhsComponent = ((GenericArrayType) rhsType).getGenericComponentType();

                return isAssignable(lhsComponent, rhsComponent);
            }
        }

        if (lhsType instanceof WildcardType) { return isAssignable((WildcardType) lhsType, rhsType); }

        return false;
    }

    private static boolean isAssignable(ParameterizedType lhsType, ParameterizedType rhsType) {
        if (lhsType.equals(rhsType)) { return true; }

        Type[] lhsTypeArguments = lhsType.getActualTypeArguments();
        Type[] rhsTypeArguments = rhsType.getActualTypeArguments();

        if (lhsTypeArguments.length != rhsTypeArguments.length) { return false; }

        for (int size = lhsTypeArguments.length, i = 0; i < size; ++i) {
            Type lhsArg = lhsTypeArguments[i];
            Type rhsArg = rhsTypeArguments[i];

            if (!lhsArg.equals(rhsArg) && !(lhsArg instanceof WildcardType
                    && isAssignable((WildcardType) lhsArg, rhsArg))) { return false; }
        }

        return true;
    }

    private static boolean isAssignable(WildcardType lhsType, Type rhsType) {
        Type[] lUpperBounds = lhsType.getUpperBounds();

        // supply the implicit upper bound if none are specified
        if (lUpperBounds.length == 0) {
            lUpperBounds = new Type[] { Object.class };
        }

        Type[] lLowerBounds = lhsType.getLowerBounds();

        // supply the implicit lower bound if none are specified
        if (lLowerBounds.length == 0) {
            lLowerBounds = new Type[] { null };
        }

        if (rhsType instanceof WildcardType) {
            // both the upper and lower bounds of the right-hand side must be
            // completely enclosed in the upper and lower bounds of the left-
            // hand side.
            WildcardType rhsWcType = (WildcardType) rhsType;
            Type[] rUpperBounds = rhsWcType.getUpperBounds();

            if (rUpperBounds.length == 0) {
                rUpperBounds = new Type[] { Object.class };
            }

            Type[] rLowerBounds = rhsWcType.getLowerBounds();

            if (rLowerBounds.length == 0) {
                rLowerBounds = new Type[] { null };
            }

            for (Type lBound : lUpperBounds) {
                for (Type rBound : rUpperBounds) {
                    if (!isAssignableBound(lBound, rBound)) { return false; }
                }

                for (Type rBound : rLowerBounds) {
                    if (!isAssignableBound(lBound, rBound)) { return false; }
                }
            }

            for (Type lBound : lLowerBounds) {
                for (Type rBound : rUpperBounds) {
                    if (!isAssignableBound(rBound, lBound)) { return false; }
                }

                for (Type rBound : rLowerBounds) {
                    if (!isAssignableBound(rBound, lBound)) { return false; }
                }
            }
        } else {
            for (Type lBound : lUpperBounds) {
                if (!isAssignableBound(lBound, rhsType)) { return false; }
            }

            for (Type lBound : lLowerBounds) {
                if (!isAssignableBound(rhsType, lBound)) { return false; }
            }
        }

        return true;
    }

    public static boolean isAssignableBound(Type lhsType, Type rhsType) {
        if (rhsType == null) { return true; }

        if (lhsType == null) { return false; }
        return isAssignable(lhsType, rhsType);
    }

}
